(1) Field of the Invention
The invention relates to a lockable retractable locating frame of a BGA (Ball grid array) on-top test socket, and more particularly to a controllable frame which utilizes a push-and-lock mechanism to block selectively downward movement of the frame and so as to freeze the position relationship between the frame and the base bearing the frame.
(2) Description of the Prior Art
In the industry of testing electronic devices, especially BGA-type electronic devices, an open-top test socket is usually utilized as an interface structure between devices under test (DUT) and the test circuiting. By providing the open-top test socket, advantages such as easy up-and-down loading of DUTs, adoptable to various packing thickness, and providing better environmental ventilation can be easily obtained.
Referring to FIG. 1, a conventional open-top test socket 20 is shown to be mounted on a test board 10 which includes the test circuiting for testing electronic devices. Also shown in the figure, a DUT 5 has already sit on the test socket 20.
Refer to both FIG. 1 and FIG. 2. The test socket 20 consists of a base 202 fixed on the test board 10, and a locating frame 201 mounted atop the base 202. The test socket 20 is shaped rectangular so as to provide an inside for constructing a ball-clipping mechanism 203. The ball-clipping mechanism 203 for positioning the DUT 5 further includes a fixed thumb set and a pairing movable forefinger set. Upon some particular arrangements, several stroke spaces 204 are formed between the base 202 and the locating frame 201. As shown in FIG. 2, those stroke spaces 204 may have different widths, but always have a common height S, the operational stroke of the test socket 20, which defines the maximum allowed distance for the locating frame 201 to move downward against the base 202.
Prior to mounting an electronic device 5 onto the ball-clipping mechanism 203 of the test socket 20, the locating frame 201 is firstly depressed evenly to move toward the base 202 along the operation stroke S such that the movable forefinger set of the ball-clipping mechanism 203 can be moved with respect to the fixed thumb set to produce predetermined spacing for receiving sparkle balls of the electronic device 5. As long as the electronic device 5 is set on the ball-clipping mechanism 203, the locating frame 201 is then released and moves automatically away the base 202 till the height S is regained. Simultaneously with the upward movement of the locating frame 201, the movable forefinger set is moved close to the fixed thumb set so as to clip each of the solder balls of the electronic device 5 in between and thus the electronic device 5 is held firmly on the test socket 20 by the ball-clipping mechanism 203.
On the other hand, while an electronic device 5 is downloaded from the test socket 20, the locating frame 201 is firstly depressed to regenerate the predetermined spacing between the fixed thumb set and the movable forefinger set of the ball-clipping mechanism 203. Thereby, the solder balls of the electronic device 5 can be released and removed from the test socket 20.
Obviously, by providing the test socket 20, the testing upon the electronic devices 5 with various package thickness, lead or ball numbers can no longer be a problem in the art.
Nevertheless, a requirement for successfully applying the test socket 20 mentioned above is that, during the testing, the locating frame 201 must be free of any forcing so as not to accidentally release the electronic device 5 under test. Referring to FIG. 3, a reason for the above requirement is that an unexpected forcing to the ball clipping mechanism 203 can shorten the distance S between the locating frame 201 and the base 202, such that a shift will be contributed to broaden the spacing between the fixed thumb set 2031 and the moveable forefinger set 2032 of the ball-clipping mechanism 203. As a consequence, the solder balls 51 of the DUT 5 held originally in position by the ball-clipping mechanism 203 will be instantly released and thereby make the DUT 5 flip up off the mechanism 203 to an incorrect position shown by the dashed DUT 5′. Definitely, in the position 5′, the testing can never be performed correctly. In particular, it is noted that the minor shift of the DUT from the correct position 5 to the fault position 5‘ is usually negligible and can’t be corrected in time.
Though the foregoing free-of-forcing requirement to the locating frame 201 may be prevented by a careful operator, yet some non-human factors, such as an unexpected shaking from the neighboring facilities, a pass-by vehicle, or an accidental impact nearby may also cause the locating frame 201 to shift and result in releasing the DUT 5 to an incorrect position. Apparently, aforesaid minor shift problem of the test socket 20 constructed as above can't be only eliminated by caution and thus is always a reason to question the testing outcome.